This invention relates to apparatus for mixing water with CO.sub.2 gas to produce carbonated water in a storage tank and operates to cool its contents and to form an ice bank on the cooling pipes of a cooling circuit in the wall area of the storage tank, whose interior also includes the placement of a circulating pump, whereby CO.sub.2 gas from the head area of the storage tank is mixed by rotation and/or circulation with the water inside the storage tank. Both fresh water and CO.sub.2 gas are fed into the head area of the storage tank while carbonated water is removed from the base or bottom of the tank.
Apparatus which mixes water with CO.sub.2 gas to produce carbonated water is well known and is used, for example, in post-mix beverage dispensing machines so that carbonated beverages can be prepared and dispensed on demand by mixing carbonated water with a suitable drink concentrate. The carbonated water mixed with the drink concentrate is produced directly in the storage tank by mixing water and CO.sub.2 gas which is fed thereto and thereafter cooled for better carbonation, this being a requirement for a cool refreshing drink which is prepared for consumption as the need arises. The storage tank, commonly referred to as a carbonator, is fed fresh water of drinking quality either from the line of a water supply system or a pressurized storage tank. The fresh water, moreover, can be fed from the water supply system under pressure and can be enhanced, when desired, by the use of a pressure pump. Further, CO.sub.2 gas is fed to the carbonator from a CO.sub.2 gas storage tank by a pressure-reducing regulating valve so that a pressure of, for example, about 4 bars is built up in the carbonator.
In order to ensure sufficient carbonation of the fresh water, the carbonation process can be accomplished by or assisted by the use of a CO.sub.2 circulating pump located in the carbonator. This type of pump draws CO.sub.2 gas from the upper or head-space region of the carbonator filled with CO.sub.2 gas and blends it with circulating water which is set in circular motion, such as by spinning.
As already noted, cooling of the carbonator is used, not only to improve the carbonation, but also as a requirement so that the finally prepared and dispensed drink exhibits a desired low and basically constant temperature. The cooling of the carbonator is achieved by a cooling system, which is adapted to form an ice bank of generally uniform thickness along the inner side walls of the carbonator as a result of the circulating water. Consequently, a cooling capacitor is produced, thus enhancing its "refrigerating capacity", thereby removing the need for a relatively powerful cooling system which would be necessary in a once-through cooling system.
Arrangements having a corresponding design as described above are well known, a typical example being shown and described in U.S. Pat. No. 5,184,942, Deininger et al, Feb. 9, 1993.
In the dispensing of a freshly prepared carbonated drink, a shutoff valve is typically opened in a line connected to the bottom of the carbonator, whereupon cooled carbonated water is fed therefrom to a concentrate mixing station. As a result, fresh water, which is relatively warmer than the carbonated water already stored in the storage tank, is fed by the feed line into the head-space region of the storage tank. Thus, immediately after the refilling process, the water in the carbonator tank is somewhat warmer than normal, particularly if a relatively large amount of water is exchanged when, for example, a large number of beverages are dispensed in a short sequence of time. The ice bank formed in the storage tank is used to specifically balance water temperature differences as quickly as possible by a partial melting of the ice bank. The time necessary for ice bank depletion is actually relatively short, but it is not short enough to make a noticeable temperature difference of the dispensed carbonated water in the case when infrequent dispensing occurs.